Spinal implant and cutting tool preparation accessory for mounting the implant

REFERENCE TO RELATED APPLICATION

0001This application claims priority to and is a divisional of U.S. patent application Ser. No. 09/486,301, filed Sep. 29, 2000 and entitled: “SPINAL IMPLANT”, now U.S. Pat. No. 6,746,484; to WO 99/09913 (PCT/IB98/01324) filed Aug. 25, 1998; and to FR97/10664 filed Aug. 26, 1997 all of which are incorporated by refrence herein in the entirety.

TECHNICAL FIELD

0002The present invention relates to spinal implant devices and associated techniques for promoting fusion of two or more vertebrae.

BACKGROUND

0003It is known that when an intervertebral disc degenerates or is damaged, there is often a compression of the disc and a reduction in the normal intervertebral height. Typically, this condition results in abnormal motions that become a source of pain.

0004In order to treat a pathology of this type, the disc is often stabilized to eliminate the abnormal motions caused by disc disorders or injuries. Generally, one approach is to prevent articulation between the two vertebrae situated on each side of the damaged disc by bone fusion. This fusion fixes the vertebrae to each other, eliminating the relative mobility causing the pain.

0005Various spinal implants to promote fusion between adjacent vertebrae have been proposed. It has been proposed to interconnect the two vertebrae by a kind of rigid U-shaped stirrup which restores the discal height with a bone graft material disposed inside the stirrup. However, one drawback of this proposal is its diminishing effectiveness over a period of time.

0006An spinal cage is also known which consists of a cylindrical member provided with a series of openings and provided with anchoring points. This implant is placed in a recess formed in the intervertebral disc and penetrates the opposite cortical plates of the two vertebrae which were previously hollowed out to receive the implant. This penetration forms openings in the sub-chondral plates to place spongy bone of the vertebrae in contact with bone graft material placed inside the implant, facilitating bone fusion. U.S. Pat. No. 5,015,247 provides one example of this approach.

0007Proper performance of a spinal implant of this type requires balancing the need to promote fusion between the spongy bone and the need to form a reliable load bearing relationship with the stronger cortical bone. As a result, the spinal cage must be neither engaged too far into the openings provided in the cortical plates to provide a sufficiently dense load bearing surface, nor insufficiently inserted, in which case the bone fusion between the two vertebrae would be adversely affected by a poor anchorage. Thus, there is a demand for devices and techniques that facilitate attaining the proper balance between fusion and load support.

0008The present invention meets this demand and provides other significant benefits and advantages.

DISCLOSURE OF THE INVENTION

0009The present invention relates to spinal fusion implants and techniques. Various aspects of the present invention are novel, nonobvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms which are characteristic of the preferred embodiments disclosed herein are described briefly as follows.

0010According to one form of the invention, the spinal implant comprises a body having a central part arranged to allow arthrodesis and at least one terminal part for bearing against the cortical bone of the vertebral end plates. The central part is adapted to penetrate the vertebral end plates, transversely projecting from the terminal bearing part. Thus the invention achieves a separation between the end parts constituting the load bearers, and the intermediate part of the implant which permits fusion. In addition, the central part may include at least one cavity for receiving a bone graft material.

0011In another form of the present invention, an implant for insertion between a first vertebra having a first cortical bone plate and a second vertebra having a second cortical bone plate includes two terminal parts. The first terminal part defines a first bearing surface to bear against the first cortical bone plate and a second bearing surface opposite the first surface to bear against the second cortical bone plate. The second terminal part opposes the first terminal part and defines a third bearing surface to bear against the first cortical bone plate and a fourth bearing surface opposite the third surface to bear against the second cortical bone plate. The implant has an elongated central part defining an upper projection extending past the first and third surfaces, and a lower projection extending past the second and fourth surfaces. These projections correspondingly pass through openings in the first and second cortical bone plates when the first and third surfaces bear against the first cortical bone plate and the second and fourth surfaces bear against the second cortical bone plate. The terminal parts are dimensioned to facilitate restoration of the natural geometry of the intervertebral space (lordosis, cyphosis, and parallel discs). Thus, the first and second surfaces may be separated by a first distance, and the third and fourth surface may be separated by a second distance greater than the first distance to accommodate a natural curvature of the spine.

0012In a further form of the present invention, an implant with two terminal parts also has an elongated central part that includes a pair of longitudinal walls defining a cavity. The walls define a first edge projecting past the first and third surfaces and a second edge projecting past the second and fourth surfaces. The first and second edges correspondingly penetrate the first and second cortical bone plates when the first and third surfaces bear against the first cortical bone plate and the second and fourth surfaces bear against the second cortical bone plate.

0013According to another form, the bearing surfaces of the terminal end parts are defined by flanges extending from opposing ends of the implant along its longitudinal axis. Preferably, the bearing surfaces are generally flat for bearing against the cortical bone of the vertebral end plates of the two adjacent vertebrae. It is also preferred that openings be cut into the cortical plates in their central regions corresponding to the length of a central part of the implant along the longitudinal axis and leaving a region of the cortical bone plates around the periphery of the openings. The length of the remaining peripheral plate corresponds to the length of the bearing surfaces along the longitudinal axis. When the implant is placed in position, the edges of the walls of the central part engage the openings cut in the cortical plates and consequently do not substantially bear against the remaining peripheral portion of the plates. A cavity may be defined by the central part that holds bone graft material in contact with the spongy bone of the two vertebrae. In contrast, the bearing surfaces of the flanges are disposed adjacent the edges of the openings of the cortical plates and bear against the remaining portions of the plates to establish a strong load bearing relationship. Thus, both bone fusion and support are distinctly accommodated by different parts of the implant structure, which permits obtaining a satisfactory support of the vertebral bodies on the implant and an excellent arthrodesis.

0014Yet another form of the present invention includes a cutting tool accessory to prepare the cortical plates of two adjacent vertebrae for insertion of an implant. This tool comprises a proximal handle connected to an elongate shaft configured to rotate about a longitudinal axis of the tool. The tool also includes a first non-cutting portion with the shaft extending therethrough and being configured to rotate relative thereto. A cutting portion is fixed to the shaft to rotate therewith and is positioned distal to the first non-cutting portion. The cutting portion includes a first pair of generally parallel opposing faces and a second pair of opposing faces each extending between the first pair of faces. The second pair of faces each define a number of cutting teeth. A second non-cutting portion is fixed to the cutting portion that includes a distal head. The first non-cutting portion, the cutting portion, and the second non-cutting portion have a rotatably selectable alignment that presents a generally constant height corresponding to the intersomatic space defined between the cortical bone plates to facilitate insertion therein. Once inserted, the cutting portion may be rotated out of this alignment to cut a first opening in the first cortical bone plate and a second opening into the second cortical bone plate. The cutting portion and to non-cutting portions may be arranged to provide uniform, symmetrical cutting of these openings with a predetermined length corresponding to the dimensions of a given implant device.

0015In an additional form, a technique of spinal fixation includes cutting adjacent vertebrae and inserting an implant therebetween to promote fusion and provide suitable support. The implant may be inserted by anterior or posterior surgical approaches. The cutting may be performed by the cutting tool of the present invention and may include initially inserting the tool so that a first pair of faces are in contact with a respective one of the first and second cortical bone plates, turning a handle to rotate the cutting portion to remove cortical bone with cutting teeth defined by a second pair of faces, and withdrawing the tool. The tool may be used to form openings readily positioned in the central region of the adjacent vertebrae that leaves cortical bone plate about the openings. The insertion of the implant may include positioning the implant of the present invention between the first and second vertebrae and turning the implant about one quarter of a turn.

0016It is envisioned that the implants of the present invention may be used with other tools and procedures, that the tools of the present invention may be used with other implants and procedures, and that the procedures of the present invention may be used with other implants and tools as would occur to those skilled in the art without departing from the spirit of the present invention.

0017Accordingly, one object of the invention is to provide a spinal implant arranged to facilitate proper fusion of two or more vertebrae. The implant may be arranged to have at least one structural part to promote bone fusion through contact with spongy vertebral bone and one or more other structural parts adapted for contact with cortical bone to provide load support.

0018Another object is to provide a tool accessory to facilitate implantation of devices suitable to promote fusion.

0019Still another object is to provide a technique for preparing a site between two vertebrae to be fused and inserting an implant.

0020Other objects, features, benefits, forms, aspects, and advantages of the present invention will become apparent from the description and drawings herein.

BRIEF DESCRIPTION OF THE DRAWINGS

0021<figref idref="DRAWINGS">FIG. 1</figref> is a perspective view, to a larger scale, of one embodiment of a spinal implant of the present invention.

0022<figref idref="DRAWINGS">FIG. 2</figref> is a perspective view of one embodiment of a cutting tool of the present invention for mounting the implant of <figref idref="DRAWINGS">FIG. 1</figref>.

0023<figref idref="DRAWINGS">FIG. 3</figref> is a perspective view of a distracting wedge or “distractor” used for carrying out a surgical method in accordance with the present invention.

0024<figref idref="DRAWINGS">FIG. 4</figref> is a partial elevational view diagrammatically illustrating the insertion of the cutting tool between two vertebrae.

0025<figref idref="DRAWINGS">FIG. 5</figref> is a partial elevation view showing the cutting tool after rotation of the cutting portion through 90° and penetrating the cortical plates of the two adjacent vertebrae.

0026<figref idref="DRAWINGS">FIG. 6</figref> is a partial sectional view taken in a sagittal plane showing the implant of <figref idref="DRAWINGS">FIG. 1</figref> positioned in an intervertebral disc for achieving a spinal fusion.

0027<figref idref="DRAWINGS">FIG. 7</figref> is a perspective view of a spinal segment in the intervertebral disc in which two implants have been installed.

MODE(S) FOR CARRYING OUT THE INVENTION

0028For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described device, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.

0029<figref idref="DRAWINGS">FIGS. 1</figref>, <b>6</b>, and <b>7</b> depict spinal cage implant <b>1</b>. Implant <b>1</b> is adapted to be inserted in a cavity provided in a damaged intervertebral disc <b>2</b> (<figref idref="DRAWINGS">FIG. 7</figref>). so as to restore the normal height of the intervertebral space between the two vertebrae V<b>1</b> and V<b>2</b> adjacent to the disc <b>2</b>, for example the lumbar vertebrae L<b>3</b>, L<b>4</b> as depicted in <figref idref="DRAWINGS">FIG. 7</figref>. <figref idref="DRAWINGS">FIG. 1</figref> shows implant <b>1</b> disposed along its longitudinal axis YY. Implant <b>1</b> comprises a hollow body <b>3</b> of elongate shape, having a central part <b>3</b><i>c </i>formed by two parallel longitudinal walls <b>4</b> arranged to permit the arthrodesis and, at the two opposite ends of the central part <b>3</b><i>c</i>, in the direction of the implantation of the implant <b>1</b>, two terminal parts <b>5</b>, <b>6</b> for bearing against the cortical bone <b>14</b> of vertebral cortical bone plates <b>15</b>, <b>16</b> of the two vertebrae (V<b>1</b>, V<b>2</b>) adjacent to the disc <b>2</b> (see, for example, <figref idref="DRAWINGS">FIG. 6</figref>).

0030The longitudinal walls <b>4</b> define therebetween a cavity <b>7</b> and are provided with openings <b>11</b>. Terminal parts <b>5</b>, <b>6</b> are disposed opposite each other along axis YY and each include a terminal face defining a centrally located threaded hole <b>11</b><i>a</i>. Holes <b>11</b><i>a </i>are configured for engagement by a threaded shaft of an insertion/manipulation accessory (no shown) to facilitate placement of implant <b>1</b> between vertebrae V<b>1</b>, V<b>2</b>. The cavity <b>7</b> is provided to receive a graft G of spongy bone or any other material favoring bone fusion, for example a synthetic ceramic.

0031Terminal part <b>5</b> has two opposite bearing surfaces <b>12</b> transverse to axis YY which are so dimensioned that they are separated by distance d<b>1</b>. Terminal part <b>6</b> has two opposite bearing surfaces <b>13</b> transverse to axis YY which are so dimensioned that they are separated by distance d<b>2</b>. Distances d<b>1</b>, d<b>2</b> are adapted to the geometry of the intervertebral space to be restored. When d<b>2</b> is greater than d<b>1</b> as depicted, implant <b>1</b> is preferred for fusion of vertebrae in a region of the spine having a natural curvature. Distance <b>1</b> corresponds to a maximum width dimension of body <b>3</b>. In one embodiment, the width of body <b>3</b> is generally constant along axis YY and is about the same as distance d<b>1</b> to facilitate a proper fit between vertebrae V<b>1</b>, V<b>2</b> as will become more apparent hereinafter.

0032The terminal parts <b>5</b>, <b>6</b> are extended by load bearing flanges <b>8</b>, <b>9</b>, namely two load bearing flanges <b>8</b> for part <b>5</b> and two load bearing flanges <b>9</b> for part <b>6</b>.

0033In the depicted embodiment, flanges <b>8</b>, <b>9</b> form parallel bars perpendicular to the longitudinal walls <b>4</b>, and define generally flat surfaces <b>12</b>, <b>13</b> for bearing against the cortical bone <b>14</b> of the vertebral end plates <b>15</b>, <b>16</b>.

0034In the illustrated embodiment, the longitudinal walls <b>4</b> have a substantially trapezoidal contour of which the small base corresponds to the terminal part <b>5</b> and the large base corresponds to the terminal part <b>6</b>. The walls <b>4</b> constituting the central part <b>3</b><i>c </i>of the implant <b>1</b> are so shaped as to transversely project from the terminal bearing parts <b>5</b>, <b>6</b>, as can be seen in <figref idref="DRAWINGS">FIGS. 1 and 6</figref>. Thus the walls <b>4</b> can penetrate respective openings <b>19</b>, <b>21</b> of the vertebral plates <b>15</b>, <b>16</b> whose edges bear against the bearing surfaces <b>12</b>, <b>13</b> of the flanges <b>8</b>, <b>9</b> (<figref idref="DRAWINGS">FIG. 6</figref>).

0035Flanges <b>8</b>, <b>9</b> are shaped to define step projections <b>17</b><i>a</i>, <b>18</b><i>a </i>to further facilitate penetration of openings <b>19</b>, <b>21</b>. Projections <b>17</b><i>a</i>, <b>18</b><i>a </i>also provide a lip to maintain alignment of bearing surfaces <b>12</b>,<b>13</b> with cortical bone plates <b>15</b>, <b>16</b> about the periphery of the openings as shown in <figref idref="DRAWINGS">FIG. 6</figref>. Walls <b>4</b> also include tapered edges <b>4</b><i>a </i>to facilitate penetration. Correspondingly, central part <b>3</b><i>c </i>has upper projection <b>3</b><i>a </i>and lower projection <b>3</b><i>b </i>defined by edges <b>4</b><i>a</i>. Notably, edges <b>4</b><i>a </i>and projections <b>3</b><i>a</i>, <b>3</b><i>b </i>transversely project away from surfaces <b>12</b>, <b>13</b>.

0036Implant <b>1</b> may be placed in position in the intervertebral disc <b>2</b> after preparation with cutting tool accessory <b>22</b> which will now be described with reference to <figref idref="DRAWINGS">FIGS. 2</figref>, <b>4</b>, and <b>5</b>. Preferably, tool <b>22</b> is made from a metallic material suitable for surgical use. Tool <b>22</b> has a milling cutter <b>23</b> including central cutting portion <b>24</b> and two non-cutting portions <b>31</b>, <b>36</b> arranged at opposite ends of central cutting portion <b>24</b>. Non-cutting portions <b>31</b>, <b>36</b> have height h corresponding to the intersomatic space and permitting uniform, symmetrical cutting of a predetermined length through a central region of both vertebral plates <b>15</b>, <b>16</b>. Preferably, the geometry of portions <b>24</b>, <b>31</b>, <b>36</b> is determined for preparing the intersomatic space with the geometry of implant <b>1</b> to restore the natural lordosis of the intervertebral space, and correspondingly the distances represented by h and d<b>1</b> are approximately equal.

0037Central cutting portion <b>24</b> has a trapezoidal shape with two generally smooth, longitudinal faces <b>25</b> opposed to each other. Faces <b>25</b> are configured to facilitate insertion into the intersomatic space being generally separated from each other by distance h. Central cutting portion <b>24</b> also has cutting faces <b>26</b> extending between faces <b>25</b>. Cutting faces <b>26</b> define a number of uniformly spaced apart cutting teeth <b>28</b>. Teeth <b>28</b> each extend along a generally straight path that is slanted at an oblique angle relative to longitudinal axis XX of tool <b>22</b>. Preferably, central cutting portion <b>24</b> is made from a suitable metallic material that has been machined to form teeth <b>28</b>.

0038Non-cutting portion <b>31</b> is fixed to the distal end of central cutting portion <b>24</b>. Portion <b>31</b> extends from central cutting portion <b>24</b> to provide a distal head in the form of a parallelepiped-shaped bar. Portion <b>31</b> has a first dimension substantially the same as distance h to be generally coextensive with faces <b>25</b> of central cutting portion <b>24</b>. Portion <b>31</b> also has opposing faces <b>32</b> separated from each other by a distance H as shown in <figref idref="DRAWINGS">FIG. 5</figref>. Preferably distance H is approximately equal to distance d<b>2</b> when tool <b>22</b> is being utilized to install implant <b>1</b>.

0039Tool <b>22</b> also includes a shaft or shank <b>33</b> connected to a proximal actuating handle <b>34</b>. Shank <b>33</b> is fixed to central cutting portion <b>24</b> and non-cutting portion <b>31</b>. Shank <b>33</b> extends from the small end face <b>27</b> remote from the non-cutting head <b>31</b> and terminates in the handle <b>34</b> which permits rotating the cutting portion <b>24</b> about the longitudinal axis XX of tool <b>22</b>.

0040Non-cutting portion <b>36</b> has a rectangular shape with generally planar faces <b>37</b>, <b>38</b>. Portion <b>36</b> may be inserted between two consecutive vertebrae during rotation of central cutting portion <b>24</b>. Portion <b>36</b> extends in the direction toward the handle <b>34</b> by a tubular part <b>40</b> and through block <b>40</b><i>a </i>which terminates in the vicinity of the handle <b>34</b>. Non-cutting portion <b>36</b> is provided with lateral stops <b>39</b> capable of being put into abutment against the sides of the vertebrae (V<b>1</b>, V<b>2</b>) after insertion therebetween. Non-cutting portion <b>36</b> encloses shank <b>33</b>. Shank <b>33</b> is configured to rotate relative to portion <b>36</b>. Correspondingly, when handle <b>34</b> is turned, shank <b>33</b>, central cutting portion <b>24</b>, and non-cutting portion <b>31</b> rotate together about axis XX with non-cutting portion <b>36</b> preferably remaining stationary. It should be noted that the partial view of <figref idref="DRAWINGS">FIGS. 4 and 5</figref> do not show handle <b>34</b> and depict a cutaway view of non-cutting portion <b>36</b> with shank <b>33</b> projecting therefrom.

0041Various nonlimiting embodiments of a spinal fixation or fusion procedure of the present invention are next described. One procedure is characterized by: (a) cutting the vertebrae V<b>1</b>, V<b>2</b> and disc <b>2</b> with tool <b>22</b> to prepare for implantation and (b) inserting the implant <b>1</b> between vertebrae V<b>1</b>, V<b>2</b>. Another more detailed procedure for fusing two vertebrae together is described in terms of procedural stages (a)-(h) as follows:

0042(a) A surgeon first separates the dural sleeve forming the extension of the bone marrow if the procedure is in the lumbar region and then carries out a discectomy to provide space for implant <b>1</b> in disc <b>2</b>.

0043(b) The surgeon inserts between the two vertebrae V<b>1</b>, V<b>2</b> from the rear (posterior), two lordosis distractors <b>41</b> as shown in <figref idref="DRAWINGS">FIG. 3</figref>. Each distractor <b>41</b> consists of a parallelepiped-shaped part <b>42</b> extended by a wedge part <b>43</b> of triangular section. Part <b>42</b> is provided with thrust plate <b>44</b>. Distractors <b>42</b> are inserted laterally with respect to the cavity provided by the discectomy of stage (a). Each distractor <b>41</b> is initially inserted by presenting its narrower aspect between V<b>1</b> and V<b>2</b>, and, then turned through 90° so as to spread apart the vertebrae and restore the discal height and the height of the considered vertebral segment. Next, one of the distractors <b>41</b> is removed.

0044(c) The surgeon inserts tool <b>22</b> between the vertebrae V<b>1</b>, V<b>2</b> as shown in <figref idref="DRAWINGS">FIG. 4</figref> so that the larger, smooth faces <b>25</b> are in contact with the vertebral plates <b>15</b>, <b>16</b>. When the cutting portion <b>24</b> is correctly positioned in the central region of the cortical plates, stops <b>39</b> come into abutment with the outer surface of the vertebrae V<b>1</b>, V<b>2</b> and non-cutting portion <b>36</b> is partly inserted between the plates <b>15</b>, <b>16</b>.

0045(d) Next, the surgeon turns handle <b>34</b>, causing cutting portion <b>24</b> to rotate about axis XX. Typically, portion <b>24</b> is rotated a number of times. As rotation continues cutting teeth <b>28</b> engage the central parts of cortical plates <b>15</b>, <b>16</b> (<figref idref="DRAWINGS">FIG. 5</figref>), gradually removing cortical bone <b>14</b>. At the end of the hollowing out of these plates, the cutting faces <b>26</b> of the central cutting portion <b>24</b> and the cutting teeth <b>28</b> have cut through the plates <b>15</b>, <b>16</b> to form generally centrally located openings <b>19</b>, <b>21</b>. Remaining portions of plates <b>15</b>, <b>16</b> then bear against the opposite faces <b>32</b> of non-cutting portion <b>31</b> and against non-cutting portion <b>36</b>.

0046(e) Then, the surgeon withdraws tool <b>22</b> from between vertebrae V<b>1</b>, V<b>2</b>.

0047(f) Next, the surgeon inserts implant <b>1</b>, previously filled with the bone graft G, between the plates <b>15</b>, <b>16</b> from the rear to a suitable position by presenting the terminal part <b>6</b> and the bearing flanges <b>9</b> at the front end. The implant <b>1</b> is presented flat, so that longitudinal walls <b>4</b> are generally parallel to the cortical plates <b>15</b>, <b>16</b> and initially come into contact therewith during insertion.

0048(g) Thereafter, the surgeon turns implant <b>1</b> through a quarter of a turn about its longitudinal axis (YY) so as to place it in the position shown in <figref idref="DRAWINGS">FIG. 6</figref> with walls <b>4</b> substantially perpendicular to the cortical plates and its flat surfaces <b>12</b>, <b>13</b> generally parallel to cortical plates <b>15</b>, <b>16</b>. Implant <b>1</b> may be inserted and turned by engaging hole <b>11</b><i>a </i>with a correspondingly threaded shaft of an accessory tool (not shown). The edges <b>4</b><i>a </i>of the longitudinal walls <b>4</b> which define projections <b>3</b><i>a</i>, <b>3</b><i>b </i>are inserted into openings <b>19</b>, <b>21</b> thereby passing through plates <b>15</b>, <b>16</b>, while remaining portions of plates <b>15</b>, <b>16</b> bear against flat surfaces <b>12</b>, <b>13</b>. Implant <b>1</b> is then in its final position in which it is stabilized. The bone graft G is in contact with the spongy part S<b>1</b>, S<b>2</b>, promoting bone fusion.

0049(h) The surgeon removes the second distractor <b>41</b> then repeats the preceding sequence of stages (a) through (g) to mount a second spinal cage implant <b>1</b> by placing it in a position generally parallel to the first cage implant <b>1</b> on the other side of the axis of the spinal column resulting in the configuration depicted in <figref idref="DRAWINGS">FIG. 7</figref> (implants <b>1</b> are shown in phantom).

0050In other embodiments, it is envisioned that the described stages may be altered, deleted, combined, repeated, or resequenced as would occur to those skilled in the art. By way of nonlimiting example, the procedure according to the present invention may utilize one or more different tools to prepare the spine for fixation by the implant of the present invention. In another example, the tool of the present invention may be utilized to prepare a surgical site for a different implant.

0051Indeed, the scope of the invention is not intended to be limited to the described embodiment and may also include variants within the scope of the accompanying claims. For example, terminal bearing surfaces <b>12</b>, <b>13</b> for the vertebral plates may have any shape, such as a curved or cylindrical shape with plates <b>15</b>, <b>16</b> being correspondingly cut so as to allow placing the bearing surfaces in a suitable position. Further, these bearing surfaces may be interconnected in pairs and constitute a single member <b>50</b> as shown in <figref idref="DRAWINGS">FIG. 6</figref>.

0052Likewise, the central part of the implant of the present invention may have any shape, preferably retaining edges that project from the terminal bearing parts. In particular, the body may have a multitude of cells. Also, it should be generally noted that the implant and tool of the present invention may be adapted to a geometry of the spine with respect to lordosis, cyphosis or parallel vertebral end plates. Thus, the present invention includes application to adjacent vertebrae other than L<b>3</b>, L<b>4</b>. Correspondingly, the implant and the cutting portion of the tool may have a different shape, such as a cylindrical geometry other than the generally conical geometry depicted. Also, Instead of using the disclosed implant <b>1</b>, the spinal space prepared by tool <b>22</b> can be filled with any other material as would occur to those skilled in the art.

0053According to other embodiments, the implant can be partly or totally constituted by porous rehabitable or resorbable materials favoring osteointegration. Such embodiments include: (a) an implant according to the above-illustrated geometry entirely made of a resorbable or rehabitable material; (b) an implant in which the whole of the central part is made of a resorbable or rehabitable material; or (c) an implant in which the periphery of the central part is made of a metallic or other material and the inside part is of a material favoring osteointegration that may be in an initially solid, pasty or liquid state.

0054In another alternative embodiment an implant is provided with only one bearing end part in which the end portion opposite to the bearing end part is open and forms a U shape for receiving a bone graft or a rehabitable or resorbable material.

0055French Patent Application Number 97 10664 filed on Aug. 26, 1997 to which priority is claimed is hereby incorporated by reference as if it were specifically set forth in its entirety herein. While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiments have been shown and described and that all changes, modifications, and equivalents that come within the spirit of the invention as defined by the following claims are desired to be protected.